The present invention relates to an automatic document feeder which is disposed in an image forming apparatus, such as an image reading apparatus and an image printing apparatus, and automatically processes operations ranged from supplying a document to ejecting the same in order to form an image.
Conventionally, there has been known an image forming apparatus provided with an automatic document feeder which is disposed in a main body of the automatic document feeder and automatically processes operations ranged from supplying a document to ejecting the same in order to form an image. And, in the automatic document feeder, especially, in case there is a plurality of original documents, it is preferable to eject the documents after being read in the same order as in the documents before being read.
On the other hand, in accordance with becoming a higher speed process in recent years, in place of a system in which the document is once stopped on a reading section to read a document by parallel transfer (scanning) of the reading apparatus along the document, there has been known an apparatus which adopts a so-called sheet-through system, that is, a system in which the document passes through the reading section of the reading apparatus to read an image of the document while the reading apparatus is fixed at the predetermined position.
As the automatic document feeder for the image forming apparatus, there has been generally known an apparatus disclosed in Japanese Patent Publication (KOKAI) No. H8-133551. By referring to FIG. 11, a summary of this automatic document feeder is explained below.
In FIG. 11, numeral 1 designates an image forming apparatus main body; 2 designates a platen glass which is disposed in the main body 1 for placing the document thereon in case of reading the thick document such as a book; 3 designates reading means, such as CCD, for reading the document on the platen glass 2; 4 designates an automatic document feeder attached to the image forming apparatus main body 1 to be able to open and close such that it covers the platen glass 2. Incidentally, 5 designates a platen glass for reading the document in case of automatic document feeding by using the automatic document feeder 4.
Here, the reading means 3 reads a document, which is transferred by automatic document feeding, at a predetermined reading position, and also, moves to read the document in case the thick document such as a book is placed on the platen glass 2.
The automatic document feeder 4 is formed of a platen cover 7 having a white sheet 6 pressing a thick document such as a book onto the platen glass 2, a document supply table 8, an ejection table 7b formed on an upper surface of the platen cover 7, and a document transfer section 9; and is disposed to freely open and close with respect to the platen glass in the image forming apparatus.
In the document transfer section 9, documents placed on the document supply table 8 are separated into one sheet by separating means 9h disposed in a document supply part 9a, and supplied, then a leading edge of the document abuts against register means 9i so as to align the documents. Then, the document transferred by the register means 9i to a transfer part 9c is supplied by rollers 9j and 9f, which are pressed against a feed roller 9b, to a reading section of the reading means 3 to be read. The read document is supplied by the feed roller 9b and a roller 9g to an ejection part 9e, and ejected onto the ejection table 7b by ejecting means 9k. Further, when a double-sided document is read, the document sent to the ejection part 9e is switched back, and again introduced to the transfer part 9c.
However, in case of reading a double-sided document in the prior art of Japanese Patent Publication No. H8-133551, in order to place the documents onto the ejection tray in the page order, the document is required to pass through the document reading section three times. Thus, even if the preceding document is not read, the document is required to pass through the document reading section; accordingly, even if reading the document is finished, a next document can not be supplied, so that there is a problem that time for exchanging documents can not be reduced.
Also, as an apparatus similar to the apparatus in Japanese Patent Publication No. H8-133551, there is an apparatus provided individually with a reversing ejection part for reversing the document and ejecting the same onto the ejection tray after a second side of the document is read such that the double-sided documents can be arranged in the page order when being ejected on the ejection tray.
In this apparatus similar to the apparatus of Japanese Patent Publication No. H8-133551, in order to transfer a single-sided document and a double-sided document without any problems, a plurality of transfer paths is required, and by providing a plurality of transfer paths, there is caused a problem such that the apparatus becomes complicated and larger, and requires a complicated control mechanism.
Incidentally, in the automatic document feeder of the sheet-through system, since there are digital method and analog method in reading the document by the image forming apparatus, the automatic document feeder is required to be able to apply both methods of reading, that is, it is preferable in view of cost that a single document feeding system can be applied in both the image forming apparatus of the digital method and the image forming apparatus of the analog method, so that mass production and inventory control can be facilitated.
The analog method is a method in which an image of the read document is fixed to a transfer paper at substantially real time when the document passes above the reading means; and the digital method is a method in which the image data of the document is once stored in a memory when the document passes above the reading apparatus, then the image is printed to the transfer paper. In the analog method, in case of making plural copies for the same document, the document is required to pass above the reading apparatus by a number corresponding to the number of the copies; accordingly, there is a problem that time for copying the document is long. In the digital method, it is required to mount a memory for storing image data recorded in a maximum document size which can be copied, for at least one sheet.
Incidentally, as described above, especially in the sheet-through type automatic document feeder, in order to correspond to both the digital image forming apparatus and the analog image forming apparatus, and at the same time, in order to have a plurality of functions such as single-sided document process, double-sided document process, and continuous reading process of the same side, a complicated structure of document paths was inevitable. Also, in accordance with securing the paths and increasing a number of members in order to ensure the complicated structure of the document paths, the apparatus main body becomes large, and moreover, there has been a problem that the cost therefor is extremely increased by complication of controlling the paths and by providing a number of sensors therefor.
Also, in case that a plurality of document sizes is mixed, by the method of detecting the document size on the document tray, only the maximum document size can be detected. Also, in case detecting means for document sizes is disposed in the transfer path of a document transferring apparatus, in order to detect the document size in the automatic document feeder side before reading an image, it is required to secure the long size detection path for allowing the detection of the maximum size which can be copied (such as a longitudinally elongate A3 size), so that the apparatus becomes larger, and there has been a problem that the apparatus is not practical.
The present invention has been made in view of the aforementioned circumstances, and while having plural functions for copying, a construction of document paths is simplified, so as to prevent making the apparatus larger and increasing cost thereof in accordance with securing supply paths and ejection paths and increasing a number of the component parts. Also, an object of the invention is to provide an automatic document feeder wherein the document size can be detected by a short supply path before reading an image, and which can be installed on both the digital image forming apparatus and the analog image forming apparatus.